Vacuum tube having all elements secured to a common substrate

ABSTRACT

A non-coplanar miniature vacuum tube triode, having its elements all formed by photo-resist techniques, and all secured to a common substrate, the cathode being formed directly in contact with the substrate over its surface, and the grid and anode being formed as crossovers, one for the cathode and the other for both cathode and grid, in parallel planes, leaving free space between each pair of the electrodes, and inherently providing intertube isolation and high gain per tube.

United States Patent- Hurvitz [4 1 Mar. 28, 1972 [54] VACUUM TUBE HAVING ALL 7 [56] References Cited ELEMENTS SECURED TO A COMMON SUBSTRATE UNITED STATES PATENTS 2,883,576 4/1959 Harries.... ..313 257 Inventor: Hyman Hurvitz, 1220 East West Highway,

Silver Spring, Md. 20910 Primary Examiner-David Schonberg Filed: No 20, 1970 Assistant Exammer-Paul A. Sacher Appl. No.: 91,309 ABSTRACT I A non-coplanar miniature vacuum tube triode, having its eleus. 01 .313/268, 313/341, 313/352, by phmp'vresist f 'F 9 313/353 a common substrate, the cathode being formed directly in contact with the substrate over its surface, and the grid and Int. CI H01] I] anode formed as crossovers one for the cathode and the Field of Search ..313/268, 269, 341, 352, 353 other for b h h d d rid, in parallel planes, leaving free i space between each pair of the electrodes, and inherently providing intertube isolation and high gain per tube.

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INVENTHR HYMAN HURVITZ VACUUM TUBE HAVING ALL ELEMENTS SECURED TO A COMMON SUBSTRATE BACKGROUND OF THE INVENTION It is known to fabricate vacuum tubes by laying down cathode, grid and anode on a common substrate by photo-resist methods and thin film deposition methods. Such tubes have co-planar elements, or they may have a cathode laid down in a slot in the substrate, the grid and anode being directly deposited on the substrate surface. A typical such device is that of Harries, British Pat. No. 795,146; U. S. Pat. No. 2,883,576. Such tubes have envisioned the advantages that each tube can be extremely small, that many tubes can be laid down on one substrate, and that IC techniques can be employed to build complex circuits including passive thin film elements connected to the tubes. While the vision is attractive, success has eluded workers in the field. In part this is because isolation of tubes from each other is difficult, and in part because the substrate collects electrons, between and about the tube elements, which render tube operation erratic, and in part because very low gain is achieved due to deficient shielding of the plate by the grid.

The present invention presents a new approach to the subject under discussion, involving the laying down of grids and anodes as crossovers. The production of crossovers separated by free space is old, in IC technology, but has heretofore been applied only to leads. By fabricating entire vacuum tubes as described, the tube electrodes are stacked vertically, conserving substrate space, but also the tube configuration is conventional. In addition, problems of collection of electrons on the substrate adjacent the grid are obviated, and for use in IC the tube control grid of each tube is wholly isolated from the anodes of other tubes, since each anode formed an isolating enclosure or Faraday cage for its grids and cathode.

At the same time the low gain which is typical of coplanar tubes is not present in the new tube since the grid surfaces extend in opposition to and in parallel to the cathode surfaces, and the anode surfaces do likewise.

It is one object of this invention to provide subminiature tubes formed by printed circuit or photo-resist techniques on an insulating substrate, in which tube configuration is generally conventional, with concomitant excellent intertube isolation, reproducibility of tube characteristics, and high gain, and to provide complete ICs including the tubes.'

SUMMARY OF THE INVENTION A vacuum tube having a cathode, a grid and an anode, all laid down in superposed planes, but all secured to one substrate surface, all formed by photo-resist technology, and providing a high G,,,.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1-6, 8-12 inclusive are views in section of the various stages of a triode, fabricated according to the present invention; and

FIG. 7 is a view in plan of the stage of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT According to the present invention, a substrate 10 has deposited on it a layer of a mixture of photo-resist and conventional thermo-emissive carbonates 11. A pattern 12, (FIG. 2) representing a cathode is then produced, by illuminating selectively and removing excess photo-resist. Pattern 12 consists of a mixture of photo-resist and emissive carbonates from which the photo-resist can be driven at a suitable stage in the process, or at once, by application of heat,.leaving a cathode deposited on substrate 10. Typical cathode dimensions may be 0.001 inch wide by 0.025 inch long by 0.001 inch thick, though precise dimensions are arbitrary. To achieve the precise required thickness the pattern 12 can be ground down, before the photo-resist is removed from the cathode, but usually the photo-resist can be spun on with adequate accuracy of thickness. Dimensions given are typical and not limiting. Relatively large tubes can be fabricated or much smaller ones, and the process permits a large number of cathodes to be fabricated in one operation on a common substrate.

The cathode pattern 12 and substrate 10 are again covered with a layer of photo-resist 13, to a thickness at which a grid is to subsist, i.e., to a depth of about 1-2 mils. This pattern is illuminated and excess resist removed, to leave a developed pattern l5, consisting'of cathode pattern 12 covered with resist top side, and at its side and ends with a spacing along the substrate of l-2 mils.

Metal, i.e., tantalum 16, is now deposited over the pattern 15 and the substrate 10, to a thickness of 200-300 A.' (FIG. 4) and the entire pattern again covered with resist 17. Metal deposit may be by sputtering. The resist is again illuminated to provide a pattern 18, covering only the grid 16, and extending beyond the edges of the grid 16 for l-2 mils. This will attain secure attachment of the edges of grid 16 to the substrate. At

the same time about 4 slots 19a extending transversely of the cathode are removed to leave a grid like exposed metal pattern as in FIG. 7. Removal of surplus exposed metal, i.e., that not required to form a grid, follows. This leaves a cathode, superposed by about four grid conductors, formed by conventional etching techniques, covered with resist and separated from each other along the length of the cathode and from the cathode, and all secured to the substrate. All remaining resist is then removed to leave a complete cathode and grid. If the process ceases as this point one has a hot cathode diode, but for a diode a grid like pattern is not needed.

The entire substrate is again covered with fresh resist 22 (FIG. 8) to a depth appropriate for ananode, i.e., about 2 mils. Optical removal then leaves the grid and cathode covered with resist 22a top and sides, as in FIG. 9. Anode metal 23 is now deposited to a thickness of 200-300 A., tantalum being suitable, this is covered with resist, 25, excess metal 23 exposed, and removed by etching, to leave the structure of FIG. 11. Removal of all resist as by heating or chemically, now leaves the completed tube, having an anode 25 secured to the substrate, as in FIG. 12, superposed over the grid and properly spaced therefrom.

The process of the presentinvention lends itself to production ofvacuum diodes and to arrays of these connected as matrices. The process also lends itself to fabrication of gaseous diodes and triodes, and to multi-grid tubes. In the case of gaseous diodes intended for display, these may be shaped, as desired, for example to form a number of a letter.

vAs many tubes as there is physical space for can be formed on a substrate, all simultaneously, which envisages that these may be interconnected by passive elements, i.e., resistances and capacitors (not shown) to form an IC. The usual evacuation and enclosing techniques may be used to form a finished vacuum tube, the cathodes of which may be heated by heating the substrate, but, the tube may have a cold cathode, or a field emission cathode or a be a gaseous conduction device. If only a few tubes are formed on a substrate, cathodes may be directly heated, for hot cathode tubes, but otherwise the entire substrate may be heated, as in Harries.

It has been assumed that grids and anodes will be thin film, in the above discussion. But rather heavy deposits may be made, and large triodes, especially if high power is desired. This implies that only a few tubes will be incorporated on the usual 3/4 inch 1 inch D substrate. But, in turn, large substrates may be used, say 3 inch by 5 inch, especially for gaseous displaydevices.

What I claim is:

l. A control device comprising an insulating substrate,

a cathodic coating of emissive material on said substrate,

a grid directly secured to said substrate and extending from said substrate over said cathodic coating and spaced from said cathodic coating, and

an anode directly secured to said substrate and extending from said substrate over said grid and spaced therefrom.

2. In a control device,

an insulating substrate,

a cathodic layer on said substrate,

an electrode constituting a metallic bridge extending entirely over said cathodic layer and spaced from said cathodic layer, and anchored only to said substrate adjacent two edges of said cathodic layer 3. A vacuum tube, including an insulating substrate,

an electron emissive planar cathode adjacent to said substrate,

a control grid superposed over and extending across and 

1. A control device comprising an insulating substrate, a cathodic coating of emissive material on said substrate, a grid directly secured to said substrate and extending from said substrate over said cathodic coating and spaced from said cathodic coating, and an anode directly secured to said substrate and extending from said substrate over said grid and spaced therefrom.
 2. In a control device, an insulating substrate, a cathodic layer on said substrate, an electrode constituting a metallic bridge extending entirely over said cathodic layer and spaced from said cathodic layer, and anchored only to said substrate adjacent two edges of said cathodic layer.
 3. A vacuum tube, including an insulating substrate, an electron emissive planar cathode adjacent to said substrate, a control grid superposed over and extending across and spatially separated from said cathode and secured to said substrate, and an anode secured to said substrate and adjoining said grid but separated therefrom.
 4. The combination according to claim 3, wherein said cathode is elongated and wherein said anode includes elements parallel with said cathode and on both sides thereof.
 5. The combination according to claim 3, wherein said anode is laid directly on said substrate. 